Nikon D5100 best settings?
What are the best setting for doing Portraits and Auto-Portraits with Nikon D5100 18-55mm?
Save us from noobs with DSLRs!
There are no, 'Best,' settings - the whole point of a camera like this is that you combine your experience with the camera's flexibility to work it out for yourself.
Learn to control depth-of-field, master exposure and experiment until you find out - angle, lighting conditions and distance are too variable to give a blanket answer.
Depends. In a studio? Outdoors? Shaded full sun? Overcast? Strobes or hot lights?
Shoot with the lens wide open at 55 mm.
Fill the cameras frame with the image you want. Cropping later reduces the possible quality of the shots when you later crop out a lot of the unneeded surrounding objects, etc.
At this point in time the "best setting" for your Nikon D5100 is sitting on a shelf while you read & study the Owner's Manual and then watch this: http://www.nikondigitutor.com/eng/d5100/index.html
Then you'll need to Google portrait lighting, portrait posing, natural light portraiture and study them.
Asking someone who has no way of knowing what conditions you'll be shooting in or what additional equipment you have is rather pointless. Photography is about knowing how to use Light, Composition, Exposure and Depth of Field to make the pictures you want to make. Its not about seeking some magical, nonexistent "best settings".
Start learning here:
LIGHT
http://photographyknowhow.com/photography-lighting/
http://photographyknowhow.com/quality-of-light-in-photography/
http://photographyknowhow.com/direction-of-light-in-photography/
COMPOSITION
http://www.photographymad.com/pages/view/10-top-photography-composition-rules
EXPOSURE
http://www.digital-photography-school.com/learning-exposure-in-digital-photography
DEPTH of FIELD
http://www.cambridgeincolour.com/...-field.htm
If all of this seems like just too much trouble then you might want to just sell your D5100 and buy a simple point & shoot.
The best thing for you to do is to sell your nice DSLR, and buy a fully automatic point and shoot camera.
With my D90 I go to Shooting Menu, Set Picture Control, and select Portrait. This seems to give best flesh tones and greatest dynamic range. It can make pictures coming out of the camera kind of dull, but it offers a lot of latitude for deepening the midtones later in software.
None.
There's no such thing as best setting. Learn photography.
For you? Put it on auto, the little green one with the camera.